1. Field of the Invention
The invention relates to elevators in general, and in particular to a traction-sheave elevator which has no mechanical counterweight running with it.
2. Description of the Invention
The most diverse types of elevators for the conveyance of passengers and/or loads are known and are used extensively. Elevators can generally be divided into three classes: traction-sheave or rope elevators, hydraulic elevators, and special solutions, such as, for example, rack, chain or spindle-gearing elevators. Furthermore, combined forms are also known, such as, for example, a hydraulic rope elevator, which is actuated via a piston-cylinder arrangement and interposed ropes.
In the case of traction-sheave elevators or rope elevators, a load-conveying means, in particular an elevator car, is suspended on a rope which is run over a so-called traction sheave. The traction sheave is motor-driven in order to move the car up or down. A counterweight, which as a rule is heavier than the load-conveying means, is normally arranged on the other end of the carrying means or rope. In order to set the load-conveying means and the counterweight in motion, there must be sufficient friction between the carrying rope and the traction sheave. The rope friction required for the drive is determined, on the one hand, by the configuration of the traction sheave, the rope and the number of ropes and, on the other hand, by the applied pressure of the rope against the traction sheave, this applied pressure in turn depending on the rope tension and thus on the weight of the load-conveying means and on the counterweight. The counterweight is normally designed in such a way that it corresponds approximately to the weight of the load-conveying means plus half the maximum useful load. Common counterweights are made of steel, reinforced concrete or the like and require a very large space in the elevator shaft on the one hand and robust guide rails for the spatial fixing on the other hand. This spatial guidance in the elevator shaft is costly and requires considerable material. In particular, it is often necessary to provide speed limiters and catching devices for the counterweight, which entail further constructional measures with requisite space, costs and material. Furthermore, the response behavior of the elevator is greatly impaired by the combined high moment of inertia of the load-conveying means and the counterweight.
During the modernization of existing elevator installations or during the integration of new elevators in existing buildings, in particular old buildings, apart from government conditions there is also often only a restricted space available.
A traction-sheave elevator without counterweight is disclosed by German Patent 105 613. In the traction-sheave elevator of the generic type, a manually adjustable tensioning device acts on a section of a carrying means. The tension force introduced into the carrying means is distributed uniformly to the two traction sheaves via deflection pulleys and a further carrying means closed upon itself.
The journal Liftreport, No. 2, 1990, pages 6-8 discloses a traction-sheave elevator which has no counterweight and in which a traction sheave is provided which, in combination with the driving gear, is arranged so as to hang as tension weight at the bottom in the ropes.
The object of the invention is to develop a traction-sheave elevator of the generic type without counterweight and having two traction sheaves in such a way that a high degree of safety in operation, in particular a high traction capacity, is ensured, while the elevator is to have dimensions which are as compact as possible, a reduced number of parts and reduced manufacturing and installation costs.